1. Field of the Invention
This invention relates to an ion beam processing method of working or processing a rotary part of a very small size, such as a rotatable shaft having a diameter of about 10 .mu.m, by an ion beam or a focused ion beam, and also relates to an ion beam processing apparatus for performing such a method.
2. Description of the Prior Art
Conventionally, when a workpiece for a component part of a very small-size machine is as small as 1 mm or less, or the configuration to be formed by the processing is on the order of .mu.m, the workpiece, because of its very small size, does not have a sufficient strength for working stresses applied by ordinary machining, and therefore the workpiece is liable to be deformed during the working. Thus, it is difficult to work such a workpiece by ordinary machining. To overcome this difficulty encountered with the machining method, there has been proposed a method (as disclosed in the first page of Nikkei Industrial Newspaper issued Nov. 27, 1989) in which a groove with a width of 300 to 1,000 .mu.m and a depth of 5-10 .mu.m is formed in a shaft material with a diameter of 5 mm, using exposure and etching steps utilizing light.
On the other hand, as a technique for forming a very small-size groove (on the order of 10 .mu.m or less) in a surface of a workpiece, there has been proposed a method utilizing a sputtering process using a focused ion beam, as disclosed in J. Vac. Sci. Technol. B6(5), Step/Oct 1988 ("The use of vector scanning for producing arbitrary surface contours with a focused ion beam"; G. Crow et al (Oregon Graduate Center)).
Also, of course, a lathe has been used for the machining by a cutting tool.
The above prior art performs the processing by two steps, that is, the exposure and the etching, and therefore has a problem that the process is a complicated. Further, with the etching, the patterns on the surface of the workpiece are all formed to the same depth, and therefore the etching is not suited for forming a groove of a complicated shape. For example, if the cross-sectional shape of the groove is tapered, a liquid can flow smoothly along the groove, and if the groove is so formed as to have a curvature, the concentration of stress on the material can be reduced; however, in the etching, unmasked portions are all removed to the same depth, and therefore it has been impossible to form a tapered groove and a curved groove.
The above prior art is directed to the formation of a complicate-shaped and very small-size groove using a focussed ion beam, and is suited for the processing of the flat surface, but is not suited for processing a rotary member.
Among constituent parts of a very small-size mechanism, there is a rotary cam. One example of such cam is shown in FIG. 3. This is a plate-like rotary cam in which r.sub.0 represents a radius of a basic circle, and r.sub.1 represents the amount of lift at the angles of 0.degree. and 180.degree.. This cam is the component part of a very small-size mechanism having the radius r.sub.0 of about 10 .mu.m, and is integral with a shaft having a radius r.sub.3 (.ltoreq.10 .mu.m), as shown in FIG. 4. It has been impossible to form such a component part by machining, etching and an ordinary ion beam processing.